The present invention relates to data storage systems, and more particularly, this invention relates to a tape volume access block (TVAB) stored to a magnetic tape volume for storing information about data sets stored to the magnetic tape volume.
Automated data storage libraries are known for providing cost effective storage and retrieval of large quantities of data. The data in automated data storage libraries is typically stored on media of data storage cartridges that are, in turn, stored at storage slots or the like inside the library in a fashion that renders the media, and its resident data, accessible for physical retrieval. Such data storage cartridges are commonly termed “removable media.” Data storage cartridge media may comprise any type of media on which data may be stored and which may serve as removable media, including but not limited to magnetic media (such as magnetic tape or disks), optical media (such as optical tape or disks), electronic media, e.g., programmable read only memory (PROM), electrically-erasable programmable read only memory (EEPROM), flash PROM, COMPACTFLASH, SMARTMEDIA, MEMORYSTICK, etc., or other suitable media. An example of a data storage cartridge that is widely employed in automated data storage libraries for mass data storage is a magnetic tape cartridge.
In addition to data storage media, automated data storage libraries typically comprise data storage drives that store data to, and/or retrieve data from, the data storage cartridge media. Further, automated data storage libraries typically comprise I/O stations at which data storage cartridges are supplied or added to, or removed from, the library. The transport of data storage cartridges between data storage slots, data storage drives, and I/O stations is typically accomplished by one or more accessors. Such accessors have grippers for physically retrieving the selected data storage cartridges from the storage slots within the automated data storage library and transporting such cartridges to the data storage drives by moving, for example, in the X and Y directions.
In a tape drive system, the drive moves the magnetic tape over the surface of the tape head at high speed. However, the magnetic tape must be wound to a proper position of the magnetic tape in order for desired information to be read from the magnetic tape. Furthermore, the magnetic tape must be wound to an end thereof in order to store additional data to the magnetic tape.
Conventionally, in an attempt to ascertain at which position the magnetic tape must be positioned in order to read data therefrom, auditing at the volume level may be performed. Auditing at the volume level makes use of either a Control Data Set (CDS), a limited audit of a labeled magnetic tape, etc.
The CDS is typically maintained by a tape management system. The CDS includes information about data sets stored to all magnetic tape cartridges in a tape library and/or across a plurality of tape libraries in an installation Note that the CDS resides in a location which is able to be accessed quickly, such as in a file or data set somewhere in host memory, on a direct access storage device (DASD), etc. That is, the CDS is not kept on the tape volume itself, but in another location which is associated with the tape volume.
When there is no CDS, a limited audit of a labeled tape may be performed, e.g., by reading all the label structures stored to the magnetic tape. Some exemplary label structures include header labels which precede a data set, trailer labels which follow a data set, etc. The label structures may include information such as the last few characters of the file name (such as 17 characters, but not so limited), a volume sequence number, a generation number, a version number, a creation date, an expiration date, etc. The audit of a tape volume using only the label structures is cumbersome and time consuming. The magnetic tape has to be positioned to the first label structure, which is then read into a memory, such as host storage. Then, the tape is positioned to the next label structure, which is read into memory, and so on for every data set on the tape. Not only is this inefficient, it requires a great deal of input/output (I/O) activity, particularly when a tape volume contains thousands or many thousands of files.